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.NET Framework

Encyclopedia : N : NE : NET : .NET Framework

The Microsoft .NET Framework is a component of the Microsoft Windows operating system. It provides a large body of pre-coded solutions to common program requirements, and manages the execution of programs written specifically for the framework. The .NET Framework is a key Microsoft offering, and is intended to be used by most new applications created for the Windows platform.

The pre-coded solutions form the framework's class library and cover a large range of programming needs in areas including the user interface, data access, cryptography, numeric algorithms, and network communications. The functions of the class library are used by programmers who combine them with their own code to produce applications.

Programs written for the .NET framework execute in a software environment that manages the program's runtime requirements. This runtime environment, which is also a part of the .NET framework, is known as the Common Language Runtime (CLR). The CLR provides the appearance of an application virtual machine, so that programmers need not consider the capabilities of the specific CPU that will execute the program. The CLR also provides other important services such as security guarantees, memory management, and exception handling.

The class library and the CLR together comprise the .NET framework. The framework is intended to make it easier to develop computer applications and to reduce the vulnerability of applications and computers to security threats. First released in 2002, it is included with current versions of Microsoft Windows, and can be installed on most older versions. The current version is 2.0, which was released in November 2005 in conjunction with Visual Studio 2005.

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Significance

For software developers, the .NET framework is one of the most significant changes to the Windows platform since its introduction. It brings into the operating system features and responsibilities that previously had been provided individually by programming languages and tools from various sources. The incorporation of the features into the OS offers a number of advantages, including:

These qualities are examined in more detail later in this article.

Rationale

The creation of the .Net framework reflects what has been learned over the years about the typical challenges that programmers face and useful approaches to those challenges.

Individual programming languages and tools led the way in proving the viability of features such as strong data typing, garbage-collected memory management, exception-based error handling, virtual machine architectures, and comprehensive class libraries. Visual Basic, Powerbuilder, the C++ Standard Template Library (STL), and other languages each implemented at least some of these features, but the Java language and its framework J2SE became the most notable success. Its popularity positioned it as a competitive threat to Microsoft. After failed attempts (due to copyright issues) to include a modified form of Java with Windows, Microsoft set out to create its own products that incorporated the best features of that and other languages. The effort resulted in the Microsoft .NET framework and its accompanying programming languages and tools.

Design goals and principal features

The .NET Framework was designed with several intentions: The design of the .NET framework is such that it supports platform independence. That is, a program written to use the framework should run without change on any type of computer for which the framework is implemented. At present, Microsoft has implemented the full framework only on the Windows operating system. Microsoft and others have implemented portions of the framework on non-Windows systems, but to date those implementations are not widely used.

.NET Framework architecture

Visual overview of the Common Language Infrastructure (CLI)
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Visual overview of the Common Language Infrastructure (CLI)

Common Language Infrastructure (CLI)

The most important component of the .NET Framework lies in the Common Language Infrastructure, or CLI. The purpose of the CLI is to provide a language agnostic platform for application development, including, but not limited to, components for: exception handling, garbage collection, security, and interoperability. Microsoft's implementation of the CLI is called the Common Language Runtime, or CLR. The CLI is composed of five primary parts:

Assemblies

The intermediate MSIL code is housed in .NET assemblies, which for the Windows implementation means a Portable Executable (PE) file or DLL. Assemblies are the .NET unit of deployment, versioning and security. The assembly can be made up of one or more files, but one of these must contain the manifest, which has the metadata for the assembly. The complete name of an assembly contains its simple text name, version number, culture and public key token; it must contain the name, but the others are optional. The public key token is generated when the assembly is created, and is a value that uniquely represents the name and contents of all the assembly files, and a private key known only to the creator of the assembly. Two assemblies with the same public key token are guaranteed to be identical. If an assembly is tampered with (for example, by hackers), the public key can be used to detect the tampering.

Metadata

All CIL is self-describing through .NET metadata. The CLR checks on metadata to ensure that the correct method is called. Metadata is usually generated by language compilers but developers can create their own metadata through custom attributes.

Base Class Library (BCL)

The Base Class Library (BCL), sometimes referred to as the Framework Class Library (FCL), is a library of types available to all languages using the .NET Framework. The BCL provides classes which encapsulate a number of common functions such as file reading and writing, graphic rendering, database interaction, XML document manipulation, and so forth. The BCL is much larger than other libraries, but has much more functionality in one package.

Security

.NET has its own security mechanism, with two general features: Code Access Security (CAS), and validation and verification. Code Access Security is based on evidence that is associated with a specific assembly. Typically the evidence is the source of the assembly (whether it is installed on the local machine, or has been downloaded from the intranet or Internet). Code Access Security uses evidence to determine the permissions granted to the code. Other code can demand that calling code is granted a specified permission. The demand causes the CLR to perform a call stack walk: every assembly of each method in the call stack is checked for the required permission and if any assembly is not granted the permission then a security exception is thrown.

When an assembly is loaded the CLR performs various tests. Two such tests are validation and verification. During validation the CLR checks that the assembly contains valid metadata and CIL, and it checks that the internal tables are correct. Verification is not so exact. The verification mechanism checks to see if the code does anything that is 'unsafe'. The algorithm used is quite conservative and hence sometimes code that is 'safe' is not verified. Unsafe code will only be executed if the assembly has the 'skip verification' permission, which generally means code that is installed on the local machine.

Standardization and Licensing

In August, 2000, Microsoft, Hewlett-Packard, and Intel worked to standardize CLI and the C# programming language. By December, 2001, both were ratified ECMA standards ([ECMA 335] and [ECMA 334]). ISO followed in April, 2003 ([ISO/IEC 23271] and [ISO/IEC 23270]).

While Microsoft and their partners hold patents for CLI and C#, ECMA and ISO requires that all patents essential to implementation be made available under "reasonable and non-discriminatory (RAND) terms." The companies have agreed to make the patents available under "royalty-free and otherwise RAND terms."

Versions

Since it was first released in 2002, Microsoft has provided two minor upgrades and one major upgrade, interspersed with several maintenance releases (known as Service Packs).

.NET Framework 1.0

Full version number - 1.0.3705

This is the initial .NET Framework, released in January 2002. It is available on its own as a redistributable package or in a software development kit. It is also part of the first release of Microsoft Visual Studio .NET (also known as Visual Studio .NET 2002).

.NET Framework 1.1

Full version number - 1.1.4322

This is the first major .NET Framework upgrade, released in April 2003. It is available on its own as a redistributable package or in a software development kit. It is also part of the second release of Microsoft Visual Studio .NET (released as Visual Studio .NET 2003). This is the first version of the .NET Framework to be included as part of the Windows operating system - it is part of Windows Server 2003.

Changes since 1.0

.NET Framework 2.0

Full version number - 2.0.50727.42 Released on November 7, 2005, along with Visual Studio 2005, SQL 2005 and BizTalk 2006.

Changes since 1.1

.NET Framework 3.0

This article or section contains information about Development_stage#Beta>beta software currently in development.
The content may change dramatically as the software development progresses.

Architecture of the .NET Framework 3.0
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Architecture of the .NET Framework 3.0

.NET Framework 3.0, formerly called WinFX[WinFX name change announcement], includes a new set of managed code APIs that are an integral part of the upcoming Windows Vista and Windows Server "Longhorn" operating systems. It will also be available for Windows XP SP2 and Windows Server 2003. There are no major architectural changes being included with this release; .NET Framework 3.0 includes version 2.0 of the Common Language Runtime.

.NET Framework 3.0 consists of four major components:

Microsoft released a Community Technology Preview of .NET Framework 3.0 on June 23 2006http://www.microsoft.com/downloads/details.aspx?FamilyID=8D09697E-4868-4D8D-A4CF-9B82A2AE542D&displaylang=en for Windows XP. The same version of the Framework is installed by default in Windows Vista build 5456, released to beta testers at around the same time.

.NET vs. Java EE

The CLI, the CIL, and C# have similarities to Sun's JVM and Java; hence, they are fierce competitors. Both use their own intermediate byte-code, Microsoft calling theirs Microsoft Intermediate Language (MSIL). MSIL is designed for just-in-time compilation (JITting), while Java bytecode is generally designed to be interpreted, not JITted (However Sun's HotSpot is a successful JIT implementation of Java). .NET is currently only fully available on Windows platforms, whereas Java is fully available on many platforms. However, Microsoft did release source code for portions of the .NET framework, including the C++ source code for some of their CLR. This forms the basis of the Shared source CLI. It along with other implementations currently in progress such as Portable.NET and Mono can be used to run some .NET applications on Unix-like operating systems such as Linux, FreeBSD, and Mac OS X. Java EE is an alternative, providing different functionality than the .NET framework and other Microsoft technologies such as COM+ (previously MTS) and MSMQ.

More cooperation is possible with the software "IKVM", which is an implementation of the Java Virtual Machine in .NET.

Java has an alternative implementation of remote procedure calls and network transparency called remote method invocation (RMI). RMI in its "RMI over IIOP" (RMI-IIOP) variant is also compatible with CORBA.

It is important to distinguish between the .Net Platform, and the individual languages (C# and VB.NET) used to develop for the platform. Similarly, the Java platform is distinct from the actual Java language, as other source languages can be compiled down to Java Byte Code. With this warning in mind, it may be useful to read a comparison of Java and C#.

Criticism

Some concerns and criticisms relating to the .NET Framework include:

Alternative implementations

The Microsoft .NET Framework is the predominent implementation of .NET technologies. Other implementations for parts of the framework exist. Since the runtime engine is described by a ECMA/ISO specification, other implementations of it are unencumbered by copyright issues. It is more difficult to develop alternatives to the base class library (BCL), which is not described by an open standard, and may be subject to copyright restrictions. Additionally, parts of the BCL have Windows-specific functionality and behavior, so implementation on non-Windows platforms can be problematic.

Some alternative implementations of parts of the framework are listed here.

See also

References

External links

Microsoft

Other

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